Lago de Atitlán is one of the rare places in the world where you can dive at altitude without using a dry suit, and ATI Divers offers trips from Santa Cruz. These include a four-day PADI open-water diving certification course (Q220), as well as a PADI high-altitude course (Q750) and fun dives (Q480) for beginners.
Courses include accommodation at it's base at La Iguana Perdida.
The lake fills a collapsed volcanic cone with bizarre geological formations and aquatic life such as cichlids, which spawn near an active fault line where hot water vents into the lake. Diving at altitude brings its own challenges – you need better control over your buoyancy, visibility is reduced and you cannot leave the lake the day of your final dive due to the change in atmospheric pressure. During the rainy season the water clouds up, so the best time to dive is between October and May.